Chapter 3 Planning Your TCP/IP Network (Task)

This chapter describes the issues you must resolve in order
to create your network in an organized, cost-effective manner. After you resolve
these issues, you can devise a plan for your network to follow as you configure
and administer your network in the future.

Determine if your network is large enough to require routers,
and, if appropriate, create a network topology that supports them.

Set up subnets, if appropriate, for your network.

The remainder of this chapter explains how to plan your network.

Setting Up an IP Address Scheme

The number of machines that you expect to support affects how you configure
your network. Your organization might require a small network of several dozen
standalone machines that are located on one floor of a single building. Alternatively,
you might need to set up a network with more than 1000 hosts in several buildings.
This arrangement can require you to further divide your network into subdivisions
that are called subnets. The size of your prospective
network affects the following factors:

Network class that you apply for

Network number that you receive

IP addressing scheme that you use for your network

Administering Network Numbers

If your organization has been assigned more than one network number,
or uses subnets, appoint a centralized authority within your organization
to assign network numbers. That authority should maintain control of a pool
of assigned network numbers, and assign network, subnet, and host numbers
as required. To prevent problems, ensure that duplicate or random network
numbers do not exist in your organization. If you are planning to transition
to IPv6, see Chapter 17, Transitioning From IPv4 to IPv6 (Reference).

Designing Your IPv4 Addressing Scheme

After you receive your network number, you can then plan how to assign
the host parts of the IPv4 address.

The following table shows the division of the IPv4 address space into
network and host address spaces. For each class, “Range” specifies
the range of decimal values for the first byte of the network number. “Network
Address” indicates the number of bytes of the IPv4 address that are
dedicated to the network part of the address. Each byte is represented by xxx. “Host Address” indicates the number of bytes
that are dedicated to the host part of the address. For example, in a class
A network address, the first byte is dedicated to the network, and the last
three bytes are dedicated to the host. The opposite designation is true for
a class C network.

Table 3–1 Division of IPv4 Address Space

Class

Range

Network Address

Host Address

A

0–127

xxx

xxx.xxx.xxx

B

128–191

xxx.xxx

xxx.xxx

C

192–223

xxx.xxx.xxx

xxx

The numbers in the first byte of the IPv4 address define whether the
network is class A, B, or C. InterNIC assigns the numbers. The remaining three
bytes have a range from 0–255. The numbers 0 and 255 are reserved. You
can assign the numbers 1–254 to each byte, depending on the
network number that is assigned to you.

The following table shows which bytes of the IPv4 address are assigned
to you. The following table also shows the range of numbers within each byte
that are available for you to assign to your hosts.

Table 3–2 Range of Available Numbers

Network Class

Byte 1 Range

Byte 2 Range

Byte 3 Range

Byte 4 Range

A

0–127

1–254

1–254

1–254

B

128–191

Preassigned by Internet

1–254

1–254

C

192–223

Preassigned by Internet

Preassigned by Internet

1–254

How IP Addresses Apply to Network Interfaces

In order to connect to the network, a computer must have at least one
network interface. Each network interface must have its own unique IP address.
The IP address that you give to a host is assigned to its network interface,
sometimes referred to as the primary network interface.
If you add a second network interface to a machine, the machine must have
its own unique IP number. When you add a second network interface, the machine
changes to a router. See Configuring Routers for an explanation.
If you add a second network interface to a host and you disable routing, the
host is then considered a multihomed host.

Each network interface has a device name, device driver, and an associated
device file in the /devices directory. The network interface
might have a device name, such as le0 or smc0, device names for two commonly used Ethernet interfaces.

Note –

This book assumes that your machines have Ethernet network interfaces.
If you plan to use different network media, refer to the manuals that come
with the network interface for configuration information.

Naming Entities on Your Network

After you receive your assigned network number and you have given the
IP addresses to your hosts, the next task is to assign names to the hosts.
Then you must determine how to handle name services on your network. You use
these names initially when you set up your network and later when you expand
your network through routers or PPP.

The TCP/IP protocols locate a machine on a network by using its IP address.
However, if you use a recognizable name, then you can identify the machine
easily. Therefore, the TCP/IP protocols (and the Solaris operating environment)
require both the IP address and the host name to uniquely identify a machine.

From a TCP/IP perspective, a network is a set of named entities. A host
is an entity with a name. A router is an entity with a name. The network is
an entity with a name. A group or department in which the network is installed
can also be given a name, as can a division, a region, or a company. In theory,
the hierarchy of names that can be used to identify a network has virtually
no limit. The name identifies a domain.

Administering Host Names

Many sites let users pick host names for their machines. Servers also
require at least one host name, which is associated with the IP address of
its primary network interface.

As network administrator, you must ensure that each host name in your
domain is unique. In other words, no two machines on your network can both
have the name “fred.” However, the machine “fred”
might have multiple IP addresses.

When planning your network, make a list of IP addresses and their associated
host names for easy access during the setup process. The list can help you
verify that all host names are unique.

Selecting a Name Service

The Solaris operating environment gives you the option of using four
types of name services: local files, NIS, NIS+, and DNS. Name services maintain
critical information about the machines on a network, such as the host names,
IP addresses, Ethernet addresses, and so forth. The Solaris operating environment
also gives you the option of using the LDAP directory service.

Network Databases

When you install the operating system, you supply the host name and
IP address of your server, clients, or standalone system as part of the procedure.
The Solaris installation program enters this information into the hosts and ipnodes network databases. These
databases are part of a set of network databases that contain information
necessary for TCP/IP operation on your network. The name service that you
select for your network reads these databases.

The configuration of the network databases is a critical. Therefore,
you need to decide which name service to use as part of the network planning
process. Moreover, the decision to use name services also affects whether
you organize your network into an administrative domain. Network Databases and nsswitch.conf File
has detailed information on the set of network databases.

Using Local Files for Name Service

If you do not implement NIS, NIS+, or DNS, the network uses local files to provide name service. The term “local files”
refers to the series of files in the /etc directory that
the network databases use. The procedures in this book assume you are using
local files for your name service, unless otherwise indicated.

Note –

If you decide to use local files as the name service for your
network, you can set up another name service at a later date.

Domain Names

Many networks organize their hosts and routers into a hierarchy of administrative
domains. If you are using NIS, NIS+, or the DNS name services, you must select
a domain name for your organization that is unique worldwide. To ensure that
your domain name is unique, you should register the domain name with the InterNIC.
If you plan to use DNS, you should register your domain name with the InterNIC.

The domain name structure is hierarchical. A new domain typically is
located below an existing, related domain. For example, the domain name for
a subsidiary company can be located below the domain of the parent company.
If the domain name has no other relationship, an organization can place its
domain name directly under one of the existing top-level domains.

The following examples show top-level domains:

.com – Commercial companies (international
in scope)

.edu – Educational institutions
(international in scope)

.gov – U.S. government agencies

.fr – France

The name that identifies your organization is one that you select, with
the provision that the name is unique.

Administrative Subdivisions

The question of administrative subdivisions deals with matters of size
and control. The more hosts and servers that you have in a network, the more
complex your management task. You might want to handle such situations by
setting up additional administrative divisions. Add networks of a particular
class. Divide existing networks into subnets. The decision about setting up
administrative subdivisions for your network is determined by the following
factors:

How large is the network?

A single administrative division can handle a single network of several
hundred hosts, all in the same physical location and requiring the same administrative
services. However, sometimes you should establish several administrative subdivisions.
Subdivisions are particularly useful if you have a small network with subnets
and the network is scattered over an extensive geographical area.

Do users on the network have similar needs?

For example, you might have a network that is confined to a single building
and supports a relatively small number of machines. These machines are divided
among a number of subnetworks. Each subnetwork supports groups of users with
different needs. In this example, you might use an administrative subdivision
for each subnet.

Registering Your Network

Before you assign IP addresses to the machines on your Solaris network,
you must obtain a network number from the InterNIC. Moreover, if you are using
administrative domains, you should register them with the InterNIC.

InterNIC and InterNIC Registration Services

The InterNIC was created in 1993 to act as a central body for Internet
information, such as:

The Internet's policies

Accessing the Internet, including training services

Resources available to Internet users, such as anonymous FTP
servers, Usenet user groups, and so on

The InterNIC also includes the InterNIC Registration Services, the organization
with which you register your TCP/IP network. The InterNIC Registration Services
provide templates for obtaining a network number and for registering your
domain. When you register, remember the following points:

The InterNIC assigns network numbers.

Note –

Do not arbitrarily assign network numbers to your network, even
if you are not attaching the network to other TCP/IP networks.

InterNIC does not assign subnet numbers. Rather, subnet numbers are
composed partly of the assigned network number and numbers that you define,
as explained in What Is Subnetting?.

You—not InterNIC—determine the domain name for
your network and then register the domain name with the InterNIC.

How to Contact the InterNIC

You can reach the InterNIC Registration Services by the following forms
of communication:

The phone number is 1–703-742-4777. Phone service is available
from 7 a.m. to 7 p.m. Eastern Standard Time. The domestic toll free phone
number is 1–800–779–1710.

Adding Routers

Recall that in TCP/IP, two types of entities exist on a network: hosts
and routers. All networks must have hosts, while not all networks require
routers. The physical topology of the network determines if you need routers.
This section introduces the concepts of network topology and routing, important
when you decide to add another network to your existing network environment.

Network Topology

Network topology describes how networks fit together. Routers are the
entities that connect networks to each other. From a TCP/IP perspective, a
router is any machine that has two or more network interfaces. However, the
machine cannot function as a router until properly configured, as described
in Configuring Routers.

Routers connect two or more networks to form larger internetworks. The
routers must be configured to pass packets between two adjacent networks.
The routers also should be able to pass packets to networks that lie beyond
the adjacent networks.

The following figure shows the basic parts of a network topology. The
first illustration shows a simple configuration of two networks that are connected
by a single router. The second illustration shows a configuration of three
networks, interconnected by two routers. In the first example, router R joins
network 1 and network 2 into a larger internetwork. In the second example,
router R1 connects networks 1 and 2. Router R2 connects networks 2 and 3.
The connections form a network that includes networks 1, 2, and 3.

Figure 3–1 Basic Network Topology

Routers join networks into internetworks. Routers also route packets
between networks that are based on the addresses of the destination network.
As internetworks grow more complex, each router must make more and more decisions
about the packet destinations.

The following figure shows a more complex case. Router R3 directly connects
networks 1 and 3. The redundancy improves reliability. If network 2 goes down,
router R3 still provides a route between networks 1 and 3. You can interconnect
many networks. However, the networks must use the same network protocols.

Figure 3–2 Providing an Additional Path Between Networks

How Routers Transfer Packets

The IP address of the recipient, a part of the packet header, determines
how the packet is routed. If this address includes the network number of the
local network, the packet goes directly to the host with that IP address.
If the network number is not the local network, the packet goes to the router
on the local network.

Routers maintain routing information in routing tables.
These tables contain the IP address of the hosts and routers on the networks
to which the router is connected. The tables also contain pointers to these
networks. When a router receives a packet, the router consults its routing
table to see if the table lists the destination address in the header. If
the table does not contain the destination address, the router forwards the
packet to another router that is listed in its routing table. Refer to Configuring Routers for detailed information on routers.

The following figure shows a network topology with three networks that
are connected by two routers.

Figure 3–3 Three Interconnected Networks

Router R1 connects networks 192.9.200 and 192.9.201. Router R2 connects
networks 192.9.201 and 192.9.202. If host A on network 192.9.200 sends a
message to host B on network 192.9.202, the following events occur:

Host A sends a packet out over network 192.9.200. The packet
header contains the IPv4 address of the recipient host B, 192.9.202.10.

None of the machines on network 192.9.200 has the IPv4 address
192.9.202.10. Therefore, router R1 accepts the packet.

Router R1 examines its routing tables. No machine on network
192.9.201 has the address 192.9.202.10. However, the routing tables do list
router R2.

R1 then selects R2 as the “next hop” router. R1
sends the packet to R2.

Because R2 connects network 192.9.201 to 192.9.202, R2 has
routing information for host B. Router R2 then forwards the packet to network
192.9.202, where host B accepts the packet.